Note: The United States Coast Guard is a quasi-military organization that operates naval craft for coastal defense and customs purposes. In peacetime it is normally subordinate to the United States Department of Homeland Security, but in wartime reports to the Department of the Navy.

The combined United States armed forces consists of 1.4 million active duty personnel along with several hundred thousands each in the Reserves and National Guard.

During and immediately after World War II, the United States military was organized along lines of command that reported to their respective service chiefs (i.e. General of the Army, Admiral of the Navy). These chiefs in turn reported to the Joint Chiefs of Staff. The Joint Chiefs of Staff was a body formed by high-level representatives of each service, who elected a Chairman to communicate with the civilian government. The Chairman of the Joint Chiefs in turn reported to the Secretary of Defense, the civilian head of the military. Both the Chairman of the Joint Chiefs and the Secretary of Defense reported to the President of the United States, who simultaneously holds the military rank of commander-in-chief.

This system lead to serious counter productive inter-service rivalry. Peacetime activities (such as procurement and creation of doctrine, etc.) were tailored for each service in isolation. Just as seriously, wartime activities of each service were planned, executed, and evaluated independently. These practices resulted in division of effort, the inability to profit from economies of scale, and inhibited the development of modern warfare doctrine.

The inability to work with other service branches was made apparent with the formulation of AirLand battle[?] doctrine in the late 1970s and early 1980s. AirLand battle was an attempt to synthesize into a single doctrine all of the capabilities of the service arms of the military. This system envisioned ground, naval, air, and space based systems acting in concert to attack and defeat an opponent in depth. Realization of this ideal was impossible due to these structural factors.

To rectify these significant problems, the Goldwater-Nichols act of 1986 provided for the complete reorganization of the United States military command structure. It was the most far-reaching organizational change since the creation of the Air Force as a separate entity in 1947.

Goldwater-Nichols changed the way each service interacted with each other. Rather than reporting to a service chief, each service reported to a commander responsible for a specific function (Transportation, Space, Special Operations), or a geographic region of the globe (Europe, Middle East, etc.), known as the commander-in-chief (CINC) (pronounced "sink"). This combined arms commander would be responsible for fielding a force capable of employing AirLand battle doctrine (or its successors), with all assets available to the military. This allowed combination of effort, integrated planning, shared procurement, and a reduction or elimination in inter-service rivalry between commanders. This addressed a major conflict with Military Science, the rule of unity of command. Individual services changed from war fighting entities into organizational and training units, responsible for readiness. Thus CENTCOM (Central Command) for example, would be assigned air, ground, and naval assets in order to achieve its objective, not the inefficient method of individual services planning, supporting, and fighting the same war.

Shared procurement caused the most notable change in the peacetime military. This allowed technological advances to be quickly suffused throughout the military, and provided other ancillary benefits (such as the interoperability of radios between services, heretofore unknown in the military). Additionally, major technological advances, such as stealth[?] and smart weapons[?] were shared between services without duplication of effort, and joint implementation of new technology allowed for joint development of supporting doctrine.

United States military organization now flows from service arm generals (such as the commander of an Army division or corps), to the appropriate regional or functional CINC. The CINC reports to the Secretary of Defense. Both the Chairman of the Joint Chiefs and the Secretary of Defense report to the president, the national CINC. This profoundly changes the role of the Joint Chiefs of Staff. It now acts as a military advisory body for the President, without operational control of any regional command. In practice, the CINC advises both the Chairman and the Secretary as to conditions in his area of responsibility. Of course, the Secretary can deputize the Chairman to supervise the CINC, as happened in the Gulf War when Richard Cheney ordered Colin Powell to command Norman Schwarzkopf.

On October 29, 2002, Secretary of Defense Donald Rumsfeld ordered the use of the term CINC to be changed to the term "combatant commander" and immediately be used when referring to regional organizations (i.e. USCENTCOM) or "commander" when talking about a specified unit such as the U.S. Strategic Command (USSTRATCOM). Rumsfeld's reason was his belief that the use of the term drew unfavorable comparisons to the President of the United States, enshrined in the Constitution as the only Commander in Chief of the Armed Forces. Changing the title was felt to properly clarify the military's role vis a vis the civilian government.

NORTHCOM's "area of responsibility" ("AOR") covers air, land and sea approaches encompassing the continental United States (including Alaska), Canada, Mexico, and the surrounding water out to approximately 500 nautical miles. It also includes the Gulf of Mexico, Puerto Rico and the U.S. Virgin Islands. Island states, territories, and possessions (including Hawaii) in the Pacific Ocean fall under the AOR of the U.S. Pacific Command. NORTHCOM provides homeland defense and coordinates homeland security with civilian forces. The commander of NORTHCOM is also the commander of North American Aerospace Defense Command (NORAD).

STRATCOM's AOR covers the strategic deterrent force (ICBMs and other nuclear weapons) of the United States. It commands all of these forces, whether air (missles and bombers), ground (artillery), or naval (nuclear strike submarines-SSBNs), regardless of location. With the merger of SPACECOM and STRATCOM in 2002, STRATCOM now also coordinates the use of space assets for support, intelligence, and command and control; this includes aerial refueling and airborne, satellite and computer network communications. Component operations include DSCS ground stations and satellites, JTF/CNO, JIOC, NNSOC and SPACEAF.